Field of the Invention
This invention relates generally to electrosurgical apparatus and more particularly to an improved intravascular catheter which can be used to effectively remove both fatty deposits and more calcified lesions from the interior walls of a blood vessel.
Discussion of the Prior Art
The buildup of atheromas or the formation of thrombi in a blood vessel can cause serious circulatory problems and when complete blockage occurs, distal tissues may be deprived of oxygen and nutrients, leading to damage or destruction of cell tissue downstream of the blockage. As the blockage grows, distal tissue may become more ischemic unless, of course, channelization occurs whereby blood bypasses the constriction. With a narrowed blood vessel, a point may be reached where even a tiny thrombus becomes lodged creating an infarct.
The treatment of diseased blood vessels depends to a large extent on the location of the blockage. In the case of a blocked or partially blocked coronary artery, it has been the practice to perform coronary bypass surgery. In a like fashion, blood vessel shunts have been installed in other body areas as well. The surgery involved in those procedures tends to be quite traumatic, involving, in the case of coronary-bypass surgery, the opening of the patient's chest and pericardium. In treating deep vein thrombosis or other blockages in the peripheral vasculature, extensive excision and vessel replacement is often required.
More recently, following the technique credited to A. Grunzig, a balloon catheter has been used to restore patency to blood vessels without extensive surgery. In carrying out this technique, a catheter having a small inflatable balloon on its distal end is routed through the vascular system to the site of the restriction to be treated. The deflated balloon is appropriately positioned to span the blockage in question and then a fluid is introduced into the proximal end of the catheter to inflate the balloon to a sufficiently high pressure whereby the blockage is spread open and patency is restored.
As is pointed out in the U.S. Pat. No. 4,445,509 to Auth, there are some deficiencies in the Grunzig procedure which renders it ineffective in certain applications. For example, the blockage may be such that it is not possible to safely force the distal tip of the catheter through the blockage prior to the inflation of the balloon. The Auth patent also cites a number of other U.S. patents relating to catheter-mounted cutting devices intended to "tunnel" through a blockage but without doing damage to the healthy blood vessel tissue. The invention of the Auth patent is in the design of a rotatably driven cutting tool which will preferentially abrade hard or calcified lesions while not significantly abrading the endothelial lining of the blood vessel.
Atherectomy catheters with rotary cutting heads are difficult and costly to make, especially given the need for providing seals on shafts moving at very high speeds. The RF ablation catheter of the present invention is substantially easier to produce in that no moving parts are involved. Also, the debris released downstream from rotating cutters may be substantial, whereas debris from RF ablation is very small and more easily tolerated by the body.